1. Field of the Invention
The present invention relates to an antenna element for supplying electric power and transmission data to wireless communications medium such as contactless IC card, and acquiring reception data from the wireless communications medium, a loop antenna using such antenna element, and a wireless communication control apparatus using such loop antenna.
2. Background Art
Hitherto, a radio-frequency identification (RF-ID) system has been known, which is designed to communicate with a wireless communications medium (such as contactless IC card) having an antenna coil without making contact, by making use of electromagnetic induction in an apparatus utilizing radio frequency electromagnetic field.
In this system, a radio frequency magnetic field is used in communications, but the radio frequency electric field is generated simultaneously with the radio frequency magnetic field. The intensity of radio frequency electric field is regulated under law, and to conform to regulation, for example, it is attempted to lower the output of antenna, but communication distance is shortened and other problems are caused. As other countermeasure, for example, as disclosed in Japanese Patent Unexamined Publication No. 2001-326526, it has been proposed to dispose a shielding plate around the antenna.
FIG. 19 is a schematic perspective view of conductive electromagnetic shield disclosed in Japanese Patent Unexamined Publication No. 2001-326526. Shield pattern for electric field 21 is wide enough to cover current feed pattern coil 22, and has an open loop for preventing generation of eddy current which disturbs generation of magnetic field, and is disposed to cover current feed pattern coil 22, and is connected to the ground. In such constitution, it is possible to decrease electric field which may disturb communications of other wireless apparatus while keeping sufficient magnetic field necessary for communications generated by transmission and reception circuit 23 and direct-current cutting capacitor 24.
In spite of such constitution, however, the electric circuit attenuates indeed, but attenuation of magnetic near field necessary in communications is large, and the communication distance becomes extremely short.